The AVuPUR project (Assessing the Vulnerabiliy of Peri-Urbans Rivers): experimental set up, modelling strategy and first results

International audienceLe projet AVuPUR a pour objectif de progresser sur la compréhension et la modélisation des flux d'eau dans les bassins versants péri-urbains. Il s'agit plus particulièrement de fournir des outils permettant de quantifier l'impact d'objets anthropiques tels que zones urbaines, routes, fossés sur les régimes hydrologiques des cours d'eau dans ces bassins. Cet article présente la stratégie expérimentale et de collecte de données mise en ½uvre dans le projet et les pistes proposées pour l'amélioration des outils de modélisation existants et le développement d'outils novateurs. Enfin, nous présentons comment ces outils seront utilisés pour simuler et quantifier l'impact des modifications d'occupation des sols et/ou du climat sur les régimes hydrologiques des bassins étudiés. / The aim of the AVuPUR project is to enhance our understanding and modelling capacity of water fluxes within suburban watersheds. In particular, the objective is to deliver tools allowing to quantify the impact of anthropogenic elements such as urban areas, roads, ditches on the hydrological regime of suburban rivers. This paper presents the observation and data collection strategy set up by the project, and the directions for improving existing modelling tools or proposing innovative ones. Finally, we present how these tools will be used to simulate and quantify the impact of land use and climate changes on the hydrological regimes of the studied catchments

The AVUPUR project (Assessing the Vulnerability of Peri-Urban Rivers)

International audienceDue to the development of urbanisation and the associated pollutions, peri-urban rivers face an increasing pressure on the receiving waters and an enhancement of floods. In order to limit the risks and define adapted management scenarios, it is important to identify the key factors over which action is possible. In particular, due to the Water Framework Directive, discharge of polluted water into rivers must be limited and actions must be undertaken in order to restore the ecological quality of water. In this context, integrated modelling tools, taking into account anthropogenic effects on the water cycle are interesting as they provide ways to test and evaluate the efficiency of different management scenarios. However improvements are still required to derive tools allowing a continuous and long term modelling of the hydrological cycle in peri-urban areas. The models must take into account the surface heterogeneity (mixture of rural and urbanised areas), and also the natural and artificial water pathways, which influence the water quality. These questions are the focus of the AVuPUR (Assessing the Vulnerability of Peri-Urban Rivers) project. Its aims are 1) to provide a better description of the heterogeneity of peri-urban catchments and of the associated water pathways using field survey, GIS and remote sensing analysis of high resolution images; 2) to provide long term detailed simulation models of the hydrological cycle in peri-urban catchments to increase our understanding of the processes involved; 3) to improve existing hydrological models with a better handling of the urbanised areas in order to derive tools usable by stakeholders; 4) to run long term simulations of the hydrological cycle using past and future land-use and climate scenarios and quantify the impact on the hydrological regime. The project focuses on two experimental catchments: the Yzeron catchment (147 km2), a peri-urban catchment located in the west of Lyon (south-east of France) and the Chézine catchment (34 km2) located close to the city of Nantes (west of France). Both catchments are part of hydrometeorological observatories which ensures a long-term monitoring of the catchments. Both catchments experience a rapid increase of urbanisation. They are located in two contrasted climates and physiographic contexts: Mediterranean type climate and marked topography for the Yzeron catchment and oceanic climate with rather flat areas for the Chézine catchment. This will allow testing the robustness and transferability of the developed approaches. The presentation will focus on the data which are currently acquired in the framework of the project: rainfall, streamflow, water levels in ephemeral reaches, lidar survey, geophysical surveys, infiltration tests. A diachronic analysis of land use since the 50th is also performed using satellite and aerial photographs. Some work is also planned to determine future land use scenarios of urbanisation and water management. Urban data bank provided by the Grand Lyon and Nantes-Métropole services are also analysed in order to document the change in water pathways due to urbanisation. The paper will present an overview of these data and first results of their analysis in terms of hydrological functioning and water pathways. The modelling strategy, which will rely on these data, will also be presented

Evaluation d'un modèle du devenir d'herbicides en parcelle drainée, développé à l'aide d'une plate-forme de modélisation environnementale

Dans le contexte de la modélisation de la pollution par les produits phytosanitaires en milieu rural, on présente un modèle local de devenir de solutés en parcelle artificiellement drainée, appelé SI#. Il simule la hauteur de nappe à l'interdrain, les débits drainé et ruisselé, ainsi que les concentrations en produits phytosanitaires dans les eaux de drainage et de ruissellement, pour des événements pluvieux correspondant à la saison de drainage intense dans le contexte pédo-climatique du Grand Ouest de la France. Le support pour son implémentation et application est la plate-forme de modélisation intégrée LIQUID®. SI# est testé par comparaison avec des données expérimentales issues du site Arvalis de La Jaillière (44), pour les produits Isoproturon et Diflufénicanil, aux échelles de l'événement pluvieux et de la saison de drainage intense. Les résultats montrent un bon comportement global de SI#, en termes de débits et de concentrations

Utilisation de la plate-forme LIQUID pour la construction d'un modèle de drainage agricole par tuyaux enterrés

[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / PHYLEAUThe LIQUID modelling framework was used to design and implement a field-scale model for subsurface tile-drainage, surface runoff and pollutant transport calculation. Three separate modules were developed to simulate the soil water dynamics in both the saturated (SIDRA) and unsaturated (SIRUP) zones as well as the solute transport into drainage and runoff water (SILASOL). Each module was built using the LIQUID template library. The modules are interconnected within the framework, using a slot-and-signal communication system allowing SIDRA, SIRUP and SILASOL to interact and interplay synchronously. The resulting model was compared with a non-modular version of the same code working with a fixed time step and experimental field data as well. The agreement between the LIQUID-based model results and field observations is more accurate, mainly because climatic forcing dynamics are better taken into account. This shows that the application of the LIQUID concepts can easily lead to an operational tool for decision makers

Modeling of hydrological processes using unstructured and irregular grids: 2D groundwater application.

18 Pags.To better handle landscape heterogeneities in distributed hydrological modeling, an earlier work proposed a discretization based on nested levels, which leads to fully unstructured modeling meshes. Upon such a discretization, traditional numerical solutions must be adapted, especially to describe lateral flow between the unstructured mesh elements. In this paper, we illustrated the feasibility of the numeric solution of the diffusion equation, representing groundwater flow, using unstructured meshes. Thus, a two-dimensional (2D) groundwater model (BOUSS2D), adapted to convex unstructured and irregular meshes was developed. It is based on the approximation of the 2D Boussinesq equation using numeric techniques suitable for nonorthogonal grids. The handling of vertical and horizontal aquifer heterogeneities is also addressed. The fluxes through the interfaces among joined mesh elements are estimated by the finite volume method and the gradient approximation method. Comparisons between the BOUSS2D predictions and analytical solutions or predictions from existing codes suggest the acceptable performance of the BOUSS2D model. These results therefore encourage the further development of hydrological models using unstructured meshes that are capable of better representing the landscape heterogeneities.Peer reviewe

Utilisation de la plate-forme LIQUID pour la construction d'un modèle de drainage agricole par tuyaux enterrés

The LIQUID modelling framework was used to design and implement a field-scale model for subsurface tile-drainage, surface runoff and pollutant transport calculation. Three separate modules were developed to simulate the soil water dynamics in both the saturated (SIDRA) and unsaturated (SIRUP) zones as well as the solute transport into drainage and runoff water (SILASOL). Each module was built using the LIQUID template library. The modules are interconnected within the framework, using a slot-and-signal communication system allowing SIDRA, SIRUP and SILASOL to interact and interplay synchronously. The resulting model was compared with a non-modular version of the same code working with a fixed time step and experimental field data as well. The agreement between the LIQUID-based model results and field observations is more accurate, mainly because climatic forcing dynamics are better taken into account. This shows that the application of the LIQUID concepts can easily lead to an operational tool for decision makers

Journal of Hydrologic Engineering

Para mejores heterogeneidades manija del paisaje en la modelización hidrológica distribuida, una obra anterior propuso una discretización basado en niveles anidados, que conduce a las mallas de modelado totalmente desestructuradas. Tras una discretización tal, soluciones numéricas tradicionales deben adaptarse, especialmente para describir el flujo lateral entre los elementos de malla no estructurados. En este artículo, ilustramos la viabilidad de la solución numérica de la ecuación de difusión, lo que representa el flujo de las aguas subterráneas, utilizando mallas no estructuradas. Por lo tanto, se desarrolló un modelo de dos dimensiones (2D) de las aguas subterráneas (BOUSS2D), adaptado a convexo mallas no estructuradas e irregulares. Se basa en la aproximación de la ecuación de Boussinesq 2D utilizando técnicas numéricas adecuadas para rejillas no ortogonales. El manejo de las heterogeneidades acuíferos verticales y horizontales también se aborda. Los flujos a través de las interfaces entre los elementos de malla unidas se estiman por el método de volúmenes finitos y el método de aproximación de gradiente. Las comparaciones entre las predicciones BOUSS2D y soluciones analíticas o predicciones de los códigos existentes sugieren que el desempeño aceptable del modelo BOUSS2D. Por tanto, estos resultados animan a un mayor desarrollo de modelos hidrológicos usando mallas no estructuradas que son capaces de una mejor representación de las heterogeneidades del paisaje.To better handle landscape heterogeneities in distributed hydrological modeling, an earlier work proposed a discretization based on nested levels, which leads to fully unstructured modeling meshes. Upon such a discretization, traditional numerical solutions must be adapted, especially to describe lateral flow between the unstructured mesh elements. In this paper, we illustrated the feasibility of the numeric solution of the diffusion equation, representing groundwater flow, using unstructured meshes. Thus, a two-dimensional 2D groundwater model BOUSS2D, adapted to convex unstructured and irregular meshes was developed. It is based on the approximation of the 2D Boussinesq equation using numeric techniques suitable for nonorthogonal grids. The handling of vertical and horizontal aquifer heterogeneities is also addressed. The fluxes through the interfaces among joined mesh elements are estimated by the finite volume method and the gradient approximation method. Comparisons between the BOUSS2D predictions and analytical solutions or predictions from existing codes suggest the acceptable performance of the BOUSS2D model. These results therefore encourage the further development of hydrological models using unstructured meshes that are capable of better representing the landscape heterogeneities.Cuenc

Utilisation de la plate-forme LIQUID pour modéliser l'influence d'aménagements hydro-agricoles sur l'hydrologie d'un petit bassin versant

Sur les petits bassins versants ruraux, la question du fonctionnement hydrologique est intimement liée à la façon dont ces bassins sont aménagés. Le façonnage du paysage par la présence humaine et l'activité agricole (découpage de parcellaire, drainage de certaines parcelles, plantation de haies en bord de parcelles, creusement de fossés) peut modifier profondément les processus hydrologiques, et avoir des conséquences importantes, notamment en termes de pollutions diffuses d'origine agricole (nutriments ou produits phytosanitaires). Si l'on veut répondre à des questions d'aménagement de ces bassins pour par exemple limiter les pollutions, on a besoin de modélisations hydrologiques précises, représentant explicitement les différents éléments du paysage susceptibles d'avoir un effet hydrologique important, y compris dans leurs formes géométriques et leurs positionnements dans l'espace